Gain stabilization of gamma-ray scintillation detector

Abstract

Systems and methods for stabilizing the gain of a gamma-ray spectroscopy system are provided. In accordance with one embodiment, a method of stabilizing the gain of a gamma-ray spectroscopy system may include generating light corresponding to gamma-rays detected from a geological formation using a scintillator having a natural radioactivity, generating an electrical signal corresponding to the light, and stabilizing the gain of the electrical signal based on the natural radioactivity of the scintillator. The scintillator may contain, for example, naturally radioactive elements such as Lutetium or Lanthanum.

1. A method comprising:
 generating light corresponding to gamma-rays detected during well logging using a detector comprising a scintillator having a natural radioactivity; 
 generating an electrical signal output from the detector corresponding to the light; and 
 stabilizing a gain of the electrical signal based on the natural radioactivity of the scintillator. 
 
     
     
       2. The method of  claim 1 , wherein generating the light comprises using a scintillator containing Lutetium. 
     
     
       3. The method of  claim 1 , wherein generating the light comprises using a scintillator containing Lanthanum. 
     
     
       4. The method of  claim 1 , wherein stabilizing the gain of the electrical signal is based at least in part on a differentiation of a background spectrum, wherein the background spectrum is a spectrum detected by the scintillator in the absence of external radiation in an energy range of interest. 
     
     
       5. The method of  claim 4 , wherein stabilizing the gain of the electrical signal comprises determining an error signal from a peak in the differentiation of the background spectrum. 
     
     
       6. The method of  claim 5 , wherein stabilizing the gain of the electrical signal comprises determining the error signal, wherein the error signal is based on the difference between two or more windows surrounding a regulation channel of the peak. 
     
     
       7. The method of  claim 1 , wherein stabilizing the gain of the electrical signal is based at least in part on a comparison to a background spectrum, wherein the background spectrum is a spectrum detected by the scintillator in the absence of an external source of radiation. 
     
     
       8. The method of  claim 7 , wherein stabilizing the gain of the electrical signal comprises adjusting the gain of the electrical signal based at least in part on the comparison to the background spectrum. 
     
     
       9. The method of  claim 1 , wherein stabilizing the gain of the electrical signal is based at least in part on a polynomial curve fitted to a background spectrum, wherein the background spectrum is a spectrum detected by the scintillator in the absence of an external source of radiation in an energy range of interest for gain regulation. 
     
     
       10. The method of  claim 1 , comprising emitting pulsed radiation from an external radiation source into a surrounding geological formation to generate the gamma-rays. 
     
     
       11. The method of  claim 10 , wherein the emitted pulsed radiation from the external radiation source comprises emitted pulsed radiation from a neutron source. 
     
     
       12. The method of  claim 10 , wherein the emitted pulsed radiation from the external radiation source comprises emitted pulsed radiation from an x-ray source. 
     
     
       13. The method of  claim 1 , wherein the method is performed in the recited order. 
     
     
       14. A gamma-ray spectroscopy system comprising:
 a detector comprising a scintillator having a natural radioactivity configured to detect gamma-rays and to output light corresponding to the gamma-rays; 
 a photodetector configured to detect the light and to output an electrical signal output from the detector corresponding to the light; and 
 signal processing circuitry configured to stabilize a gain of the electrical signal based on the natural radioactivity of the scintillator. 
 
     
     
       15. The system of  claim 14 , wherein the scintillator contains Lutetium, Lanthanum, or Bismuth Germanium Oxide. 
     
     
       16. The system of  claim 14 , wherein the signal processing circuitry is configured to stabilize the gain of the electrical signal based at least in part on a differentiation of a background spectrum, wherein the background spectrum is a spectrum detected by the scintillator in the absence of an external source of radiation. 
     
     
       17. The system of  claim 16 , wherein the signal processing circuitry is configured to determine an error signal from a peak in the differentiation of the background spectrum. 
     
     
       18. The system of  claim 17 , wherein the error signal is based on the difference between two or more windows surrounding a regulation channel of the peak. 
     
     
       19. The system of  claim 14 , wherein the signal processing circuitry is configured to compare a spectrum represented by the electrical signal to a background spectrum, wherein the background spectrum is a spectrum detected by the scintillator in the absence of an external source of radiation. 
     
     
       20. The system of  claim 19 , wherein the signal processing circuitry is configured to adjust the gain of the electrical signal based at least in part on the comparison of the spectrum represented by the electrical signal to the background spectrum. 
     
     
       21. The system of  claim 14 , wherein the signal processing circuitry is configured to stabilize the gain based at least in part on a polynomial curve fitted to a background spectrum, wherein the background spectrum is a spectrum detected by the scintillator in the absence of an external source of radiation. 
     
     
       22. The system of  claim 14 , comprising an external source configured to emit pulsed radiation into a surrounding geological formation to generate the gamma-rays, wherein the signal processing circuitry is configured to stabilize the gain during time intervals when external radiation emitted is low. 
     
     
       23. A method comprising:
 measuring a spectrum of nuclear radiation in a low background environment using a detector comprising a scintillator having a natural radioactivity; and 
 stabilizing a gain of the measured spectrum at the detector based on the natural radioactivity of the scintillator. 
 
     
     
       24. The method of  claim 23 , wherein measuring the spectrum comprises using a scintillator containing Lanthanum. 
     
     
       25. The method of  claim 23 , wherein stabilizing the gain of the measured spectrum comprises performing coarse gain regulation before performing refined gain regulation with a windows algorithm involving two or more windows. 
     
     
       26. The method of  claim 23 , wherein stabilizing the gain of the measured spectrum comprises stabilizing the gain around a regulation channel of approximately 1470 keV. 
     
     
       27. Signal processing circuitry for a spectroscopy system comprising:
 a processor configured to process a spectrum signal from a detector comprising a scintillator having a natural radioactivity; and 
 a memory device configured to supply instructions to the processor to stabilize the gain of the spectrum signal based on the natural radioactivity of the scintillator intrinsic to the detector. 
 
     
     
       28. The signal processing circuitry of  claim 27 , wherein the memory device is configured to supply instructions to the processor to stabilize the gain of the spectrum signal based at least in part on a differentiation of a background spectrum, wherein the background spectrum is a spectrum detected by the scintillator in the absence of an external source of radiation. 
     
     
       29. A method comprising:
 detecting a spectrum of nuclear radiation during well logging using a detector comprising a scintillator having a natural radioactivity; and 
 stabilizing the gain of the spectrum based on the natural radioactivity of the scintillator intrinsic to the detector. 
 
     
     
       30. The method of  claim 29 , comprising emitting pulsed radiation from an external radiation source into a surrounding geological formation to generate the nuclear radiation, wherein the gain is stabilized during time intervals when the radiation emitted is low.